Vibrating device and image equipment having the same

ABSTRACT

A vibrating device includes a dust-screening member shaped like a plate as a whole, a vibrating member arranged outside the dust-screening member and configured to produce, at the dust-screening member, vibration having a vibrational amplitude perpendicular to a surface of the dust-screening member, a counter member spaced apart from that surface of the dust-screening member, on which the vibrating member is arranged, a pushing member configured to push the dust-screening member onto the counter member, and a first support member arranged between the counter member and the dust-screening member, surrounding a center of the dust-screening member, and configured to support the dust-screening member when pushed by the pushing member. The first support member is pushed with a pressure of 2 N or less when the pushing member pushes the first support member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2009-058096, filed Mar. 11, 2009;and No. 2009-263999, filed Nov. 19, 2009, the entire contents of both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to image equipment having image formingelements such as an image sensor element or a display element, and alsoto a vibrating device designed to vibrate the dust-screening member thatis arranged at the front of each image forming element of such an imageequipment.

2. Description of the Related Art

As image equipment having image forming elements, there is known animage acquisition apparatus that has an image sensor element configuredto produce a video signal corresponding to the light applied to itsphotoelectric conversion surface. Also known is an image projector thathas a display element, such as liquid crystal element, which displays animage on a screen. In recent years, image equipment having such imageforming elements have been remarkably improved in terms of imagequality. If dust adheres to the surface of the image forming elementsuch as the image sensor element or display element or to the surface ofthe transparent member (optical element) that is positioned in front ofthe image forming element, the image produced will have shadows of thedust particles. This makes a great problem.

For example, digital cameras of called “lens-exchangeable type” havebeen put to practical use, each comprising a camera body and aphotographic optical system removably attached to the camera body. Thelens-exchangeable digital camera is so designed that the user can usevarious kinds of photographic optical systems, by removing thephotographic optical system from the camera body and then attaching anyother desirable photographic optical system to the camera body. When thephotographic optical system is removed from the camera body, the dustfloating in the environment of the camera flows into the camera body,possibly adhering to the surface of the image sensor element or to thesurface of the transparent member (optical element), such as a lens,cover glass or the like, that is positioned in front of the image sensorelement. The camera body contains various mechanisms, such as a shutterand a diaphragm mechanism. As these mechanisms operate, they producedust, which may adhere to the surface of the image sensor element aswell.

Projectors have been put to practical use, too, each configured toenlarge an image displayed by a display element (e.g., CRT or liquidcrystal element) and project the image onto a screen so that theenlarged image may be viewed. In such a projector, too, dust may adhereto the surface of the display element or to the surface of thetransparent member (optical element), such as a lens, cover glass or thelike, that is positioned in front of the display element, and enlargedshadows of the dust particles may inevitably be projected to the screen.

Various types of mechanisms that remove dust from the surface of theimage forming element or the transparent member (optical element) thatis positioned in front of the image sensor element, provided in suchimage equipment have been developed.

In an electronic image acquisition apparatus disclosed in, for example,U.S. Pat. No. 7,324,149, a ring-shaped piezoelectric element (vibratingmember) is secured to the circumferential edge of a glass plat shapedlike a disc (dust-screening member). When a voltage of a prescribedfrequency is applied to the piezoelectric element, the glass plat shapedlike a disc undergoes a standing-wave, bending vibration having nodes atthe concentric circles around the center of the glass plat shaped like adisc. This vibration removes the dust from the glass disc. The vibrationproduced by the voltage of the prescribed frequency is a standing wavehaving nodes at the concentric circles around the center of the disc.The dust-screening member is supported by dust-screening member holdingmembers and a pushing member that is a leaf spring. The dust-screeningmember holding members, which are aligned on a circle, contact thedust-screening member at the nodes of standing waves that form theconcentric circles. The pushing member pushes the dust-screening member,at those parts that contact the dust-screening member holding members.

Jpn. Pat. Appln. KOKAI Publication No. 2007-267189 discloses arectangular dust-screening member and piezoelectric elements secured tothe opposite sides of the dust-screening member, respectively. Thepiezoelectric elements produce vibration at a predetermined frequency,resonating the dust-screening member. Vibration is thereby achieved insuch mode that nodes extend parallel to the sides of the dust-screeningmember. In order to remove dust from the nodes of vibration, thedust-screening member is resonated at different frequencies,accomplishing a plurality of standing-wave vibrational modes, therebychanging the positions of nodes. Any one of the vibrational modesachieves bending vibration having nodes extending parallel to the sidesof the dust-screening member. With regarding to support of thedust-screening member, standing waves of different frequencies, eachhaving nodes almost aligned with those of any other standing wave, aregenerated, and the dust-screening member holding members support thedust-screening member at positions near the nodes of these standingwaves. The loss of vibrational energy is thereby decreased. Further, aframe-shaped seal having a lip-like cross section is interposed betweenthe image capturing surface and the dust-screening member, preventingdust from sticking to the image capturing surface.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda vibrating device comprising:

a dust-screening member shaped like a plate as a whole;

a vibrating member arranged outside the dust-screening member andconfigured to produce, at the dust-screening member, vibration having avibrational amplitude perpendicular to a surface of the dust-screeningmember;

a counter member spaced apart from that surface of the dust-screeningmember, on which the vibrating member is arranged;

a pushing member configured to push the dust-screening member onto thecounter member; and

a first support member arranged between the counter member and thedust-screening member, surrounding a center of the dust-screeningmember, and configured to support the dust-screening member when pushedby the pushing member, wherein

the first support member is pushed with a pressure of 2 N or less whenthe pushing member pushes the first support member.

According to a second aspect of the present invention, there is providedan image equipment comprising:

an image forming element having an image surface on which an opticalimage is formed;

a dust-screening member shaped like a plate as a whole, having alight-transmitting region at least spreading to a predetermined region,facing the image surface and spaced therefrom by a predetermineddistance;

a vibrating member configured to produce vibration having an amplitudeperpendicular to a surface of the dust-screening member, the vibratingmember being provided on the dust-screening member, outside thelight-transmitting region through which a light beam forming an opticalimage on the image surface passes;

a counter member spaced apart from the dust-screening member; and

a first support member arranged between the counter member and thedust-screening member, surrounding a center of the dust-screeningmember, and configured to support the dust-screening member when pushedby the dust-screening member, wherein

the first support member is pushed with a pressure of 2 N or less.

Advantages of the invention will be set forth in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the invention. Advantages of the invention may berealized and obtained by means of the instrumentalities and combinationsparticularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram schematically showing an exemplary systemconfiguration, mainly electrical, of a lens-exchangeable, single-lensreflex electronic camera (digital camera) that is a first embodiment ofthe image equipment according to this invention;

FIG. 2A is a vertical side view of an image sensor element unit of thedigital camera, which includes a dust removal mechanism (or a sectionalview taken along line A-A shown in FIG. 2B);

FIG. 2B is a front view of the dust removal mechanism, as viewed fromthe lens side;

FIG. 3 is an exploded perspective view showing a major component(vibrator) of the dust removal mechanism;

FIG. 4A is a front view of a dust filter, explaining how the dust filteris vibrated;

FIG. 4B is a sectional view of the dust filter, taken along line B-Bshown in FIG. 4A;

FIG. 4C is a sectional view of the dust filter, taken along line C-Cshown in FIG. 4A;

FIG. 5 is a diagram explaining the length of the long sides and that ofthe short sides of the dust filter;

FIG. 6A is a diagram explaining the concept of vibrating the dustfilter;

FIG. 6B is a front view of the dust filter vibrated in such a mode thatnode areas, where vibration hardly occurs, form a lattice pattern;

FIG. 7 is a diagram explaining how the dust filter is vibrated inanother mode;

FIG. 8 is a diagram showing the relation between the aspect ratio of thedust filter shown in FIG. 4A and the vibration speed ratio of the centerpart of the dust filter;

FIG. 9 is a diagram explaining how the dust filter is vibrated in stillanother mode;

FIG. 10 is a graph showing the relation between the pushing forceapplied to the dust filter and the vibration speed ratio at the centerof the dust filter;

FIG. 11 is a diagram showing another configuration the dust filter mayhave;

FIG. 12 is a diagram showing still another configuration the dust filtermay have;

FIG. 13A is a vertical sectional view (taken along line A-A in FIG. 13B)of the image sensor unit including a dust-screening mechanism that has adisc-shaped dust filter;

FIG. 13B is a front view of the dust-screening mechanism having adisc-shaped dust filter, as viewed from the lens side;

FIG. 14 is a conceptual diagram of the dust filter, explaining thestanding wave that is produced in the dust filter;

FIG. 15A is a diagram showing an electric equivalent circuit that drivesthe vibrator at a frequency near the resonance frequency;

FIG. 15B is a diagram showing an electric equivalent circuit that drivesthe vibrator at the resonance frequency;

FIG. 16 is a circuit diagram schematically showing the configuration ofa dust filter control circuit;

FIG. 17 is a timing chart showing the signals output from the componentsof the dust filter control circuit;

FIG. 18A is the first part of a flowchart showing an exemplary camerasequence (main routine) performed by the microcomputer for controllingthe digital camera body according to the first embodiment;

FIG. 18B is the second part of the flowchart showing the exemplarycamera sequence (main routine);

FIG. 19 is a flowchart showing the operating sequence of “silentvibration” that is a subroutine shown in FIG. 18A;

FIG. 20 is a flowchart showing the operation sequence of the “displayprocess” performed at the same time Step S201 of “silent vibration,”i.e. subroutine (FIG. 19), is performed;

FIG. 21 is a flowchart showing the operating sequence of the “displayprocess” performed at the same time Step S203 of “silent vibration,”i.e., or subroutine (FIG. 19), is performed;

FIG. 22 is a flowchart showing the operating sequence of the “displayprocess” performed at the same time Step S205 of “silent vibration,”i.e., subroutine (FIG. 19), is performed;

FIG. 23 is a diagram showing the form of a resonance-frequency wavecontinuously supplied to vibrating members during silent vibration; and

FIG. 24 is a flowchart showing the operating sequence of “silentvibration,” i.e., subroutine in the operating sequence of the digitalcamera that is a second embodiment of the image equipment according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Best modes of practicing this invention will be described with referenceto the accompanying drawings.

First Embodiment

An image equipment according to this invention, which will beexemplified below in detail, has a dust removal mechanism for the imagesensor element unit that performs photoelectric conversion to produce animage signal. Here, a technique of improving the dust removal functionof, for example, an electronic camera (hereinafter called “camera” willbe explained. The first embodiment will be described, particularly inconnection with a lens-exchangeable, single-lens reflex electroniccamera (digital camera), with reference to FIGS. 1 to 2B.

First, the system configuration of a digital camera 10 according to thisembodiment will be described with reference to FIG. 1. The digitalcamera 10 has a system configuration that comprises body unit 100 usedas camera body, and a lens unit 200 used as an exchange lens, i.e., oneof accessory devices.

The lens unit 200 can be attached to and detached from the body unit 100via a lens mount (not shown) provided on the front of the body unit 100.The control of the lens unit 200 is performed by the lens-controlmicrocomputer (hereinafter called “Lucom”) 201 provided in the lens unit200. The control of the body unit 100 is performed by the body-controlmicrocomputer (hereinafter called “Bucom” 101 provided in the body unit100. By a communication connector 102, the Lucom 210 and the Bucom 101are electrically connected to each other, communicating with each other,while the lens unit 200 remains attached to the body unit 100. The Lucom201 is configured to cooperate, as subordinate unit, with the Bucom 101.

The lens unit 200 further has a photographic lens 202, a diaphragm 203,a lens drive mechanism 204, and a diaphragm drive mechanism 205. Thephotographic lens 202 is driven by a DC motor (not shown) that isprovided in the lens drive mechanism 204. The diaphragm 203 is driven bya stepping motor (not shown) that is provided in the diaphragm drivemechanism 205. The Lucom 201 controls these motors in accordance withthe instructions made by the Bucom 101.

In the body unit 100, a penta-prism 103, a screen 104, a quick returnmirror 105, an ocular lens 106, a sub-mirror 107, a shutter 108, an AFsensor unit 109, an AF sensor drive circuit 110, a mirror drivemechanism 111, a shutter cocking mechanism 112, a shutter controlcircuit 113, a photometry sensor 114, and a photometry circuit 115 arearranged as shown in FIG. 1. The penta-prism 103, the screen 104, thequick return mirror 105, the ocular lens 106, and the sub-mirror 107 aresingle-lens reflex components that constitute an optical system. Theshutter 108 is a focal plane shutter arranged on the photographicoptical axis. The AF sensor unit 109 receives a light beam reflected bythe sub-mirror 107 and detects the degree of defocusing.

The AF sensor drive circuit 110 controls and drives the AF sensor unit109. The mirror drive mechanism 111 controls and drives the quick returnmirror 105. The shutter cocking mechanism 112 biases the spring (notshown) that drives the front curtain and rear curtain of the shutter108. The shutter control circuit 113 controls the motions of the frontcurtain and rear curtain of the shutter 108. The photometry sensor 114detects the light beam coming from the penta-prism 103. The photometrycircuit 115 performs a photometry process on the basis of the light beamdetected by the photometry sensor 114.

In the body unit 100, an image acquisition unit 116 is further providedto perform photoelectric conversion on the image of an object, which haspassed through the above-mentioned optical system. The image acquisitionunit 116 is a unit composed of a CCD 117 that is an image sensor elementas an image forming element, an optical low-pass filter (LPF) 118 thatis arranged in front of the CCD 117, and a dust filter 119 that is adust-screening member. Thus, in this embodiment, a transparent glassplate (optical element) that has, at least at its transparent part, arefractive index different from that of air is used as the dust filter119. Nonetheless, the dust filter 119 is not limited to a glass plate(optical element). Any other member (optical element) that exists in theoptical path and can transmit light may be used instead. For example,the transparent glass plate (optical element) may be replaced by anoptical low-pass filter (LPF), an infrared-beam filter, a deflectionfilter, a half mirror, or the like. In this case, the frequency anddrive time pertaining to vibration and the position of a vibrationmember (later described) are set in accordance with the member (opticalelement). The CCD 117 is used as an image sensor element. Nonetheless,any other image sensor element, such as CMOS or the like, may be usedinstead.

As mentioned above, the dust filter 119 can be selected from variousdevices including an optical low-pass filter (LPF). However, thisembodiment will be described on the assumption that the dust filter is aglass plate (optical element).

To the circumferential edge of the dust filter 119, two piezoelectricelements 120 a and 120 b are attached. The piezoelectric elements 120 aand 120 b have two electrodes each. A dust filter control circuit 121,which is a drive unit, drives the piezoelectric elements 120 a and 120 bat the frequency determined by the size and material of the dust filter119. As the piezoelectric elements 120 a and 120 b vibrate, the dustfilter 119 undergoes specific vibration. Dust can thereby be removedfrom the surface of the dust filter 119. To the image acquisition unit116, an anti-vibration unit is attached to compensate for the motion ofthe hand holding the digital camera 10.

The digital camera 10 according to this embodiment further has a CCDinterface circuit 122, a liquid crystal monitor 123, an SDRAM 124, aFlash ROM 125, and an image process controller 126, thereby to performnot only an electronic image acquisition function, but also anelectronic record/display function. The CCD interface circuit 122 isconnected to the CCD 117. The SDRAM 124 and the Flash ROM 125 functionas storage areas. The image process controller 126 uses the SDRAM 124and the Flash ROM 125, to process image data. A recording medium 127 isremovably connected by a communication connector (not shown) to the bodyunit 100 and can therefore communicate with the body unit 100. Therecording medium 127 is an external recording medium, such as one ofvarious memory cards or an external HDD, and records the image dataacquired by photography. As another storage area, a nonvolatile memory128, e.g., EEPROM, is provided and can be accessed from the Bucom 101.The nonvolatile memory 128 stores prescribed control parameters that arenecessary for the camera control.

To the Bucom 101, there are connected an operation display LCD 129, anoperation display LED 130, a camera operation switch 131, and a flashcontrol circuit 132. The operation display LCD 129 and the operationdisplay LED 130 display the operation state of the digital camera 10,informing the user of this operation state. The operation display LED129 or the operation display LED 130 has, for example, a display unitconfigured to display the vibration state of the dust filter 119 as longas the dust filter control circuit 121 keeps operating. The cameraoperation switch 131 is a group of switches including, for example, arelease switch, a mode changing switch, a power switch, which arenecessary for the user to operate the digital camera 10. The flashcontrol circuit 132 drives a flash tube 133.

In the body unit 100, a battery 134 used as power supply and apower-supply circuit 135 are further provided. The power-supply circuit135 converts the voltage of the battery 134 to a voltage required ineach circuit unit of the digital camera 10 and supplies the convertedvoltage to the each circuit unit. In the body unit 100, too, a voltagedetecting circuit (not shown) is provided, which detects a voltagechange at the time when a current is supplied from an external powersupply though a jack (not shown).

The components of the digital camera 10 configured as described aboveoperate as will be explained below. The image process controller 126controls the CCD interface circuit 122 in accordance with theinstructions coming from the Bucom 101, whereby image data is acquiredfrom the CCD 117. The image data is converted to a video signal by theimage process controller 126. The image represented by the video signalis displayed by the liquid crystal monitor 123. Viewing the imagedisplayed on the liquid crystal monitor 123, the user can confirm theimage photographed.

The SDRAM 124 is a memory for temporarily store the image data and isused as a work area in the process of converting the image data. Theimage data is held in the recording medium 127, for example, after ithas been converted to JPEG data.

The mirror drive mechanism 111 is a mechanism that drives the quickreturn mirror 105 between an up position and a down position. While thequick return mirror 105 stays at the down position, the light beamcoming from the photographic lens 202 is split into two beams. One beamis guide to the AF sensor unit 109, and the other beam is guided to thepenta-prism 103. The output from the AF sensor provided in the AF sensorunit 109 is transmitted via the AF sensor drive circuit 110 to the Bucom101. The Bucom 101 performs the distance measuring of the known type. Inthe meantime, a part of the light beam, which has passed through thepenta-prism 103, is guided to the photometry sensor 114 that isconnected to the photometry circuit 115. The photometry circuit 115performs photometry of the known type, on the basis of the amount oflight detected by the photometry sensor 114.

The image acquisition unit 116 that includes the CCD 117 will bedescribed with reference to FIGS. 2A and 2B. Note that the hatched partsshown in FIG. 2B show the shapes of members clearly, not to illustratingthe sections thereof.

As described above, the image acquisition unit 116 has the CCD 117, theoptical LPF 118, the dust filter 119, and the piezoelectric elements 120a and 120 b. The CCD 117 is an image sensor element that produces animage signal that corresponds to the light applied to its photoelectricconversion surface through the photographic optical system. The opticalLPF 118 is arranged at the photoelectric conversion surface of the CCD117 and removes high-frequency components from the light beam comingfrom the object through the photographic optical system. The dust filter119 is a dust-screening member arranged in front of the optical LPF 118and facing the optical LPF 118, spaced apart therefrom by apredetermined distance. The piezoelectric elements 120 a and 120 b arearranged on the circumferential edge of the dust filter 119 and arevibrating members for applying specific vibration to the dust filter119.

The CCD chip 136 of the CCD 117 is mounted directly on a flexiblesubstrate 137 that is arranged on a fixed plate 138. From the ends ofthe flexible substrate 137, connection parts 139 a and 139 b extend.Connectors 140 a and 140 b are provided on a main circuit board 141. Theconnection parts 139 a and 139 b are connected to the connectors 140 aand 140 b, whereby the flexible substrate 137 is connected to the maincircuit board 141. The CCD 117 has a protection glass plate 142. Theprotection glass plate 142 is secured to the flexible substrate 137,with a spacer 143 interposed between it and the flexible substrate 137.

Between the CCD 117 and the optical LPF 118, a filter holding member 144made of elastic material is arranged on the front circumferential edgeof the CCD 117, at a position where it does not cover the effective areaof the photoelectric conversion surface of the CCD 117. The filterholding member 144 abuts on the optical LPF 118, at a part close to therear circumferential edge of the optical LPF 118. The filter holdingmember 144 functions as a sealing member that maintains the junctionbetween the CCD 117 and the optical LPF 118 almost airtight. A holder145 is provided, covering seals the CCD 117 and the optical LPF 118 inairtight fashion. The holder 145 has a rectangular opening 146 in a partthat is substantially central around the photographic optical axis. Theinner circumferential edge of the opening 146, which faces the dustfilter 119, has a stepped part 147 having an L-shaped cross section.Into the opening 146, the optical LPF 118 and the CCD 117 are fittedfrom the back. In this case, the front circumferential edge of theoptical LPF 118 contacts the stepped part 147 in a virtually airtightfashion. Thus, the optical LPF 118 is held by the stepped part 147 at aspecific position in the direction of the photographic optical axis. Theoptical LPF 118 is therefore prevented from slipping forwards from theholder 145. The level of airtight sealing between the CCD 117 and theoptical LPF 118 is sufficient to prevent dust from entering to form animage having shadows of dust particles. In other words, the sealinglevel need not be so high as to completely prevent the in-flow ofgasses.

On the front circumferential edge of the holder 145, a dust-filterholding unit 148 is provided, covering the entire front circumferentialedge of the holder 145. The dust-filter holding unit 148 is formed,surrounding the stepped part 147 and projecting forwards from thestepped part 147, in order to hold the dust filter 119 in front of theLPF 118 and to space the filter 119 from the stepped part 147 by apredetermined distance. The opening of the dust-filter holding unit 148serves as focusing-beam passing area 149. The dust filter 119 is shapedlike a polygonal plate as a whole (a square plate, in this embodiment).The dust filter 119 is supported on a seal 150 (a first support member),pushed onto the seal 150 by a pushing member 151 which is constituted byan elastic body such as a leaf spring and has one end fastened withscrews 152 to the dust-filter holding unit 148. More specifically, acushion member 153 made of vibration attenuating material, such asrubber or resin, and adhered to the pushing member 151, is interposedbetween the pushing member 151 and the dust filter 119. On the otherhand, at the back of the dust filter 119, the seal 150 having anring-shaped lip part 150 a surrounding the center of the dust filter 119is interposed between the circumferential part of the dust filter 119and the dust-filter holding unit 148. The pushing member 151 exerts apushing force, which bends the lip part 150 a. The lip part 150 a pushesthe dust filter 119. As a result, the space including the opening 146 issealed airtight and the dust filter 119 is supported.

The dust filter 119 is positioned with respect to the Y-direction in theplane that is perpendicular to the optical axis, as that part of thepushing member 151 which is bent in the Z-direction, receive a forcethrough a positioning member 154. On the other hand, the dust filter 119is positioned with respect to the X-direction in the plane that isperpendicular to the optical axis, as a support part 155 provided on theholder 145 receive a force through the positioning member 154, as isillustrated in FIG. 2B. The positioning member 154 is made ofvibration-attenuating material such as rubber or resin, too, not toimpede the vibration of the dust filter 119. The main body 150 b of theseal 150 is pressed onto the outer circumferential edge of a ring-shapedprojection 145 a fitted at the rim of the opening 146 of the holder 145,and is thereby set in place.

When the dust filter 119 receives gravitational acceleration G and anexternal force (such as an inertial force) as the camera is moved, theexternal force is applied to the pushing member 151 or the seal 150. Thepushing member 151 is a plate made of phosphor bronze or stainlesssteel, either for use as material of springs, and has high flexuralrigidity. By contrast, the seal 150 is made of rubber and has smallflexural rigidity. Thus, the seal 150 is deformed due to the externalforce.

Cushion members 156 (second support members) made of vibrationattenuating material, such as rubber or soft resin, are provided on thatsurface of the dust-filter holding unit 148, which faces the back of thedust filter 119. At least two cushion members 156 (four cushion membersin this embodiment) are positioned, almost symmetric with respect to theoptical axis, and are spaced by distance AZ from the dust filter 119 inthe direction of the optical axis. When the seal 150 is deformed by thedistance AZ, the dust filter 119 contacts the cushion member 156. As aresult, the external force tends to compress the cushion member 156 (atfour parts). However, the cushion member 156 is scarcely deformeddespite the external force, because its compression rigidity is higherthan the flexural rigidity of the seal 150. Therefore, the seal 150 isdeformed, but very little. Note that the cushion member 156 is arranged,supporting the dust filter 119 at the nodes where the dust filter 119scarcely undergoes vibration even if the dust filter 119 is pushed bythe cushion member 156. Since the cushion member 156 is arranged so, thevibration of the dust filter 119 is not much impeded. This helps toprovide a dust-screening mechanism having that generate vibration atlarge amplitude and hence can remove dust at high efficiency. Moreover,the deformation of the seal 150, caused by the external force, is assmall as ΔZ (for example, 0.1 to 0.2 mm). Hence, an excessively largeforce will not applied to the seal 150 to twist the seal 150, failing tomaintain the airtight state, or the seal 150 will not contact the dustfilter 119 with an excessive pressure when the external force isreleased from it.

The seal 150 may of course have its main body 150 b secured to theholder 145 by means of, for example, adhesion. If the seal 150 is madeof soft material such as rubber, it may be secured to the dust filter119. In this case, the seal 150 only needs to apply a pressing forcelarge enough to support the vibrator configured by the dust filter 119and the piezoelectric elements 120 a and 120 b.

If the vibrator has a mass W (kg) and if the gravitational accelerationis 1G, the vibrator will receive a force of 1G*W (N) because of its ownweight. Assume that acceleration of 1G is also exerted on the vibratorwhile the camera is being used in normal state. Then, the total force of2WG (N) is exerted on the vibrator. To support the vibrator in thiscondition, the pushing force F (N) must be equal to or greater than 2WG(≧2WG).

In order to hold the vibrator, however, the pushing force F(N) must beabout ten times the acceleration of 2G (i.e., 2G*10=20G), including amargin, or at least 20G*W (that is, F(N)≧20G*W).

The equipment according to this embodiment, such as a digital camera,incorporates a vibrator having a mass of about 1 to 10 grams. Hence,0.198≦F (N)≦1.96, or preferably 0.2≦F (N)≦2, including a margin.Therefore, the pushing force is sufficient if it is equal to or lessthan 2 (N).

Note that the piezoelectric element used in this embodiment has a massof 1.5 grams. Hence, the pushing force is about 0.3 (N).

Therefore, as will be described later, the pressure never impede thevibration generated in the dust filter 119, and the dust filter 119 canremove dust at a very high efficiency.

The pushing force may be applied at only one position, not a pluralityof positions as in this embodiment, if the light applied toward theimage sensor is not blocked. In the configuration of FIG. 2B, forexample, the force may be applied to the piezoelectric element 120 aonly or to the piezoelectric element 120 b only.

If piezoelectric elements are arranged at a plurality of positions, thenthe piezoelectric element 120 a may so arranged as shown in, forexample, FIG. 2B, whereas the piezoelectric element 120 b may bearranged, extending perpendicular to the piezoelectric element 120 a(but not blocking the light applied toward the image sensor).

Further, piezoelectric elements may be arranged to form a rectangularframe, in a region where they do not block the light applied toward theimage sensor).

Moreover, as shown in FIG. 2B, the lip part 150 a of the seal 150 isshaped like a ring, arced at the four corners and having no inflectionpoints. So shaped, the lip part 150 a is not locally deformed when itreceives an external force.

The image acquisition unit 116 is thus configured as an airtightstructure that has the holder 145 having a desired size and holding theCCD 117. The level of airtight sealing between the dust filter 119 andthe dust-filter holding unit 148 is sufficient to prevent dust fromentering to form an image having shadows of dust particles. The sealinglevel need not be so high as to completely prevent the in-flow ofgasses.

To the ends of the piezoelectric elements 120 a and 120 b, which arevibrating members, flexes 157 a and 157 b, i.e., flexible printedboards, are electrically connected. The flexes 157 a and 157 b input anelectric signal (later described) from the dust filter control circuit121 to the piezoelectric elements 120 a and 120 b, causing the elements120 a and 120 b to vibrate in a specific way. The flexes 157 a and 157 bare made of resin and cupper etc., and have flexibility. Therefore, theylittle attenuate the vibration of the piezoelectric elements 120 a and120 b. The flexes 157 a and 157 b are provided at positions where thevibrational amplitude is small (at the nodes of vibration, which will bedescribed later), and can therefore suppress the attenuation ofvibration. The piezoelectric elements 120 a and 120 b move relative tothe body unit 100 if the camera 10 has such a hand-motion compensatingmechanism as will be later described. Hence, if the dust filter controlcircuit 121 is held by a holding member formed integral with the bodyunit 100, the flexes 157 a and 157 b are deformed and displaced as thehand-motion compensating mechanism operates. In this case, the flexes157 a and 157 b effectively work because they are thin and flexible. Inthe present embodiment, the flexes 157 a and 157 b have a simpleconfiguration, extending from two positions. They are best fit for usein cameras having a hand-motion compensating mechanism.

The dust removed from the surface of the dust filter 119 falls onto thebottom of the body unit 100, by virtue of the vibration inertia and thegravity. In this embodiment, a base 158 is arranged right below the dustfilter 119, and holding members 159 a and 159 b made of, for example,adhesive tape, is provided on the base 158. The holding members 159 aand 159 b reliably trap the dust fallen from the dust filter 119,preventing the dust from moving back to the surface of the dust filter119.

The hand-motion compensating mechanism will be explained in brief. Asshown in FIG. 1, the hand-motion compensating mechanism is composed ofan X-axis gyro 160, a Y-axis gyro 161, a vibration control circuit 162,an X-axis actuator 163, a Y-axis actuator 164, an X-frame 165, a Y-frame166 (holder 145), a frame 167, a position sensor 168, and an actuatordrive circuit 169. The X-axis gyro 160 detects the angular velocity ofthe camera when the camera moves, rotating around the X axis. The Y-axisgyro 161 detects the angular velocity of the camera when the camerarotates around the Y axis. The vibration control circuit 162 calculatesa value by which to compensate the hand motion, from theangular-velocity signals output from the X-axis gyro 160 and Y-axis gyro161. In accordance with the hand-motion compensating value thuscalculated, the actuator drive circuit 169 moves the CCD 117 in theX-axis direction and Y-axis direction, which are first and seconddirections orthogonal to each other in the XY plane that isperpendicular to the photographic optical axis, thereby to compensatethe hand motion, if the photographic optical axis is taken as Z axis.More precisely, the X-axis actuator 163 drives the X-frame 165 in theX-axis direction upon receiving a drive signal from the actuator drivecircuit 169, and the Y-axis actuator 164 drives the Y-frame 166 in theY-axis direction upon receiving a drive signal from the actuator drivecircuit 169. That is, the X-axis actuator 163 and the Y-axis actuator164 are used as drive sources, the X-frame 165 and the Y-frame 166(holder 145) which holds the CCD 117 of the image acquisition unit 116are used as objects that are moved with respect to the frame 167. Notethat the X-axis actuator 163 and the Y-axis actuator 164 are eachcomposed of an electromagnetic motor, a feed screw mechanism, and thelike. Alternatively, each actuator may be a linear motor using a voicecoil motor, a linear piezoelectric motor or the like. The positionsensor 168 detects the position of the X-frame 165 and the position ofthe Y-frame 166. On the basis of the positions the position sensor 168have detected, the vibration control circuit 162 controls the actuatordrive circuit 169, which drives the X-axis actuator 163 and the Y-axisactuator 164. The position of the CCD 117 is thereby controlled.

The dust removal mechanism of the first embodiment will be described indetail, with reference to FIGS. 3 to 14. The dust filter 119 has atleast one side symmetric with respect to a certain symmetry axis, and isa glass plate (optical element) of a polygonal plate as a whole (asquare plate, in this embodiment). The dust filter 119 has a regionflaring in the radial direction from the position at which maximumvibrational amplitude is produced. This region forms a transparent part.Alternatively, the dust filter 119 may be D-shaped, formed by cutting apart of a circular plate, thus defining one side. Still alternatively,it may formed by cutting a square plate, having two opposite sidesaccurately cut and having upper and lower sides. The above-mentionedfastening mechanism fastens the dust filter 119, with the transparentpart opposed to the front of the LPF 118 and spaced from the LPF 118 bya predetermined distance. To one surface of the dust filter 119 (i.e.,back of the filter 119, in this embodiment), the piezoelectric elements120 a and 120 b, which are vibrating members, are secured at the upperand lower edges of the filter 119, by means of adhesion using adhesive.The piezoelectric elements 120 a and 120 b, which are arranged on thedust filter 119, constitute a vibrator 170. The vibrator 170 undergoesresonance when a voltage of a prescribed frequency is applied to thepiezoelectric elements 120 a and 120 b. The resonance achieves suchbending vibration of a large amplitude, as illustrated in FIGS. 4A to4C.

As shown in FIG. 3, signal electrodes 171 a and 172 a are formed on thepiezoelectric element 120 a, and signal electrodes 171 b and 172 b areformed on the piezoelectric element 120 b. Note that the hatched partsshown in FIG. 3 show the shapes of the signal electrodes clearly, not toillustrating the sections thereof. The signal electrodes 172 a and 172 bare provided on the back opposing the signal electrodes 171 a and 171 b,and are bent toward that surface of the piezoelectric element 120 a, onwhich the signal electrodes 171 a and 171 b are provided. The flex 157 ahaving the above-mentioned conductive pattern is electrically connectedto the signal electrode 171 a and signal electrode 172 a. The flex 157 bhaving the above-mentioned conductive pattern is electrically connectedto the signal electrode 171 b and signal electrode 172 b. To the signalelectrodes 171 a, 171 b, 172 a and 172 b, a drive voltage of theprescribed frequency is applied form the dust filter control circuit 121through flexes 157 a and 157 b. The drive voltage, thus applied, cancause the dust filter 119 to undergo such a two-dimensional,standing-wave bending vibration as is shown in FIGS. 4A to 4C. The dustfilter 119 is dimensioned such that the long sides are of length LA andthe short sides are of length LB orthogonal to the long sides. (Thissize notation accords with the size notation used in FIG. 5.) Since thedust filter 119 shown in FIG. 4A is rectangular, it is identical inshape to the “virtual rectangle” according to this invention (laterdescribed). Hence, the long sides LA of the dust filter 119 areidentical to the sides LF of the virtual rectangle that include thesides LA. The bending vibration shown in FIG. 4A is standing wavevibration. In FIG. 4A, the blacker the streaks, each indicating a nodearea 173 of vibration (i.e., area where the vibrational amplitude issmall), the smaller the vibrational amplitude is. Note that the meshesshown in FIG. 4A are division meshes usually used in the final elementmethod.

If the node areas 173 are at short intervals as shown in FIG. 4A whenthe vibration speed is high, in-plane vibration (vibration along thesurface) will occur in the node areas 173. This vibration induces alarge inertial force in the direction of the in-plane vibration (seemass point Y2 in FIG. 14, described later, which moves over the nodealong an arc around the node, between positions Y2 and Y2′) to the dustat the node areas 173. If the dust filter 119 is inclined to becomeparallel to the gravity so that a force may act along the dust receivingsurface, the inertial force and the gravity can remove the dust from thenode areas 173.

In FIG. 4A, the white areas indicate areas where the vibrationalamplitude is large. The dust adhering to any white area is removed bythe inertial force exerted by the vibration. The dust can be removedfrom the node areas 173, too, by producing vibration in another mode(for example, the vibrational mode illustrated in FIG. 9), at similaramplitude at each node area 173.

The bending vibrational mode shown in FIG. 4A is achieved bysynthesizing the bending vibration of the X-direction and the bendingvibration of the Y-direction. The fundamental state of this synthesis isshown in FIG. 6A. If the vibrator 170 is put on a member that littleattenuates vibration, such as a foamed rubber block, and then made tovibrate freely, a vibrational mode of producing such lattice-shaped nodeareas 173 as shown in FIG. 6B will be usually attained easily. In thefront view included in FIG. 6A, the broken lines define the centers ofthe node areas 173 shown in FIG. 6B (more precisely, the lines indicatethe positions where the vibrational amplitude is minimal in thewidthwise direction of lines). In this case, a standing wave, bendingvibration at wavelength λ_(x) occurs in the X-direction, and a standingwave, bending vibration at wavelength λ_(y) occurs in the Y-direction.These standing waves are synthesized as shown in FIG. 6B. With respectto the origin (x=0, y=0), the vibration Z (x, y) at a given point P (x,y) is expressed by Equation 1, as follows:

Z(x,y)=A·W _(mn)(x,y)·cos(γ)+A·W _(nm)(x,y)·sin(γ)  (1)

where A is amplitude (a fixed value here, but actually changing with thevibrational mode or the power supplied to the piezoelectric elements); mand n are positive integers including 0, indicating the order of naturalvibration corresponding to the vibrational mode; γ is a given phaseangle;

${{W_{mn}( {x,y}\; )} = {{\sin ( {{n\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{m\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};$and${W_{n\; m}( {x,y} )} = {{\sin ( {{m\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {{\sin ( {{n\; {\pi \cdot y}} + \frac{\pi}{2}} )}.}}$

Assume that the phase angle γ is 0 (y=0). Then, Equation 1 changes to:

$\begin{matrix}{{Z( {x,y} )} = {A \cdot {W_{mn}( {x,y} )}}} \\{= {A \cdot {\sin ( {\frac{n \cdot \pi \cdot x}{\lambda_{x}} + \frac{\pi}{2}} )} \cdot {{\sin ( {\frac{m \cdot \pi \cdot y}{\lambda_{y}} + \frac{\pi}{2}} )}.}}}\end{matrix}$

Further assume that λ_(x)=λ_(y)=λ=1 (x and y are represented by the unitof the wavelength of bending vibration). Then:

$\begin{matrix}{{Z( {x,y} )} = {A \cdot {W_{{mn}\;}( {x,y} )}}} \\{= {A \cdot {\sin ( {{n \cdot \pi \cdot x} + \frac{\pi}{2}} )} \cdot {{\sin ( {{m \cdot \pi \cdot y} + \frac{\pi}{2}} )}.}}}\end{matrix}$

Similarly, if γ=π/2, too, the front term of the equation (1) will bezero. Hence, a similar standing wave is generated. FIG. 6A shows thevibrational mode that is applied if m=n (since the X-direction vibrationand the Y-direction vibration are identical in terms of order andwavelength, the dust filter 119 has a square shape). In this vibrationalmode, the peaks, nodes and valleys of vibration appear at regularintervals in both the X-direction and the Y-direction, and vibrationnode areas 173 appear as a checkerboard pattern (conventionalvibrational mode). In the vibrational mode where m=0, n=1, the vibrationhas peaks, nodes and valleys parallel to a side (LB) that extendsparallel to the Y-direction. In the vibrational mode described above,the X-direction vibration and the Y-direction vibration are generated,independent of each other. Even if the X-direction vibration and theY-direction vibration are synthesized, the amplitude of vibration (orvibration speed) will have the same value as in the case where onlyX-direction vibration is generated (forming nodes and peaks and valleys,all parallel to the side LB) or the case where only Y-directionvibration is generated (forming nodes and peaks and valleys, allparallel to the side LA). This takes place, also in the vibration modeshown in FIG. 6B. In these vibrational modes, the phase angle γ is k×π/2(γ=k×π/2) as pointed out before, if k is 0 or an integer (eitherpositive or negative). That is, in these vibrational modes, cos γ andsin γ are 0.

A vibrational mode in which the phase angle γ has a different value willbe explained. In view of this, the dust filter 119 may be elongated alittle, shaped like a rectangle, and may be vibrated at a specificfrequency, or in a mode where m=3 and n=2. In this vibrational mode, thephase angle γ is +π/4 or ranges from −π/4 to −π/8. This vibrational modeis a mode in which the present embodiment will have very largevibrational amplitude (the maximum amplitude is at the same level as atthe conventional circular dust filter). If γ=+π/4, the vibrational modewill be the mode shown in FIG. 4A. In this vibrational mode, the peakridges 174 of vibrational amplitude form closed loops around the opticalaxis though the dust filter 119 is rectangular. Consequently, areflected wave coming from a side extending in the X-direction and areflected wave coming from a side extending in the Y-direction areefficiently combined, forming a standing wave. FIG. 7 shows avibrational mode in which γ=−π/4 and which is achieved by changing thevibrational frequency of the dust filter 119 of FIG. 4A. In thisvibrational mode, peak ridges 174 of vibrational amplitude are formed,surrounding the midpoint of each side. That is, the center of the dustfilter 119 becomes a node area 173 where vibrational amplitude isscarcely observed. Peak ridges 174 of vibrational amplitude are formed,surrounding the midpoint of each side.

The dust filter 119 of the vibrator 170, shown in FIG. 4A, is a glassplate (optical element) having a size of 30.8 mm (X-direction: LA,LF)×28.5 mm (Y-direction: LB)×0.65 mm (thickness). The dust filter 119is rectangular, having long sides LA (30.8 mm, extending in theX-direction) and short sides LB (28.5 mm). Therefore, the dust filter119 is identical to the “virtual rectangle” according to this invention,which has the same area as the dust filter 119. The long sides LA of thedust filter 119 are arranged are thus identical to the sides LF of thevirtual rectangle that includes the sides LA. The piezoelectric elements120 a and 120 b are made of lead titanate-zirconate ceramic and have asize of 21 mm (X-direction: LP)×3 mm (Y-direction)×0.8 mm (thickness).The piezoelectric elements 120 a and 120 b are adhered with epoxy-basedadhesive to the dust filter 119, extending along the upper and lowersides of the filter 119 (optical element), respectively. Morespecifically, the piezoelectric elements 120 a and 120 b extend in theX-direction and arranged symmetric in the left-right direction, withrespect to the centerline of the dust filter 119, which extends in theY-direction. In this case, the resonance frequency in the vibrationalmode of FIG. 4A is in the vicinity of 91 kHz. At the center of the dustfilter 119, a maximal vibration speed and vibrational amplitude can beattained if the dust filter is shaped like a circle in which therectangular dust filter 119 is inscribed. The vibration-speed ratio,which is the ratio of maximum speed V_(max) to the speed of vibrationperpendicular to the plane of the center part of the dust filter 119,has such a value as shown in FIG. 8, the maximum value of which is1.000. In the graph of FIG. 8, the line curve pertains to the case wherethe piezoelectric elements 120 a and 120 b are arranged parallel to thelong sides of the dust filter 119, and the dots pertain to the casewhere the 120 a and 120 b are arranged parallel to the short sides ofthe dust filter 119. In this vibrational mode, the piezoelectricelements 120 a and 120 b should better be arranged at the longer sidesof the dust filter 119. A higher vibration speed can be achieved thanotherwise.

As described above, the phase angle γ is +π/4 or ranges from −π/4 to−π/8. Nevertheless, the phase angle need not have such a precise value.If the phase angle γ differs a little from such value, the vibrationalamplitude can be increased. Even in the vibrational mode of FIG. 9, inwhich the phase angle γ is a little smaller than +π/4, the peak ridges174 of vibrational amplitude form closed loops around the optical axis,too, and the vibration speed decreases in the Z-direction at the centerof the vibrator 170. This dust filter 119 is a glass plate (opticalelement) that has a size of 30.8 mm (X-direction: LA)×28.5 mm(Y-direction: LB)×0.65 mm (thickness). The dust filter 119 isrectangular, having long sides LA (30.8 mm, extending in theX-direction) and short sides LB (28.5 mm). Therefore, the dust filter119 is identical to the “virtual rectangle” according to this invention,which has the same area as the dust filter 119. The piezoelectricelements 120 a and 120 b have a size of 30 mm (X-direction)×3 mm(Y-direction)×0.8 mm (thickness), having a length almost equal to thelength LF (in the X-direction) of the dust filter 119, and are made oflead titanate-zirconate ceramic. The piezoelectric elements 120 a and120 b are adhered with an epoxy-based adhesive to the dust filter 119,extending along the upper and lower sides of the filter 119,respectively, and positioned symmetric in the X-direction with respectto the centerline of the dust filter 119. In this case, the resonancefrequency in the vibrational mode shown in FIG. 9 is in the vicinity of68 kHz. As in FIGS. 2A and 2B, in this case, too, the dust filter 119 issupported by the lip part 150 a of the seal 150, and the holder 145 hasfour cushion members 156, which act as second support members if anexternal force is applied to the seal 150.

The relation the pushing force applied to the dust filter 119 and thevibration speed at the center part of the dust filter 119 have in theconfiguration shown in FIGS. 2A and 2B is shown in FIG. 10. In FIG. 10,“mode 1” is the vibrational mode shown in FIG. 4A, “mode 3” is thevibrational mode shown in FIG. 9, and “mode 2” is a vibrational modehaving a phase angle γ that is halfway between those of modes 1 and 3.FIG. 10 shows how the vibration speed changes with the pressure exertedto the dust filter 119 in the case where the vibrator 170 having such alarge vibrational amplitude (vibration speed) as shown in FIG. 4A issupported.

As seen from FIG. 10, the smaller the pushing force is, the more thevibration speed will increase. If the pushing force is 2 N or less, thechange in the vibration speed ratio will sharply decrease. The vibrationspeed can be 90% or more of the maximum vibration speed, having almostthe same value as in the case where the pushing force is virtually zero.This holds true of the case where the vibrational mode is changed, andis an ideal state for supporting the vibrator 170. The vibrator 170weighs about 1.5 g. Thus, the vibrator 170 can therefore acquire about70% of the maximum vibration speed even if it receives an external forceof 1.5 N that is equivalent to gravitational acceleration of about 10 G,and the cushion members 156 therefore receive a pressing force of 3.5 N.The vibrator 170 may receive a force greater than this while the surfaceof the dust filter 119 is being cleaned. Nonetheless, the dust filter119 is not vibrated during the cleaning of the dust filter 119, causingno problems.

FIG. 11 shows a modification of the vibrator 170. The modified vibrator170 has a dust filter 119 that is D-shaped, formed by cutting a part ofa plate shaped like a disc, thus defining one side. That is, themodified vibrator 170 uses a D-shaped dust filter 119 that has a sidesymmetric with respect to the symmetry axis extending in theY-direction. The piezoelectric element 120 a is arranged on the surfaceof the dust filter 119, extending parallel to that side and positionedsymmetric with respect to the midpoint of the side (or to a symmetryaxis extending in the Y-direction). On the other hand, the piezoelectricelement 120 b is substantially inscribed in the outer circumference ofthe dust filter 119 and extends parallel to that side of the dust filter119. So shaped, the dust filter 119 is more symmetric with respect toits center (regarded as the centroid), and can more readily vibrate in astate desirable to the present embodiment. In addition, the dust filter119 can be smaller than the circular one. Furthermore, since thepiezoelectric elements 120 a and 120 b arranged parallel to the side,the asymmetry in terms vibration, resulting from the cutting, can bemade more symmetric by increasing the rigidity. This helps to render thevibration state more desirable. Note that the long side and short sideshown in FIG. 11 are the long and short sides of a virtual rectangle 175which has the same area as the dust filter 119, one side of whichincludes the above-mentioned one side of the dust filter 119, and theopposite side of which extends along an outer side of the piezoelectricelement 120 b.

The dust filter 119 is supported because the seal 150 shaped like adeformed track as viewed in the front view is arranged and held betweena holder (not shown) and the dust filter 119 and is pushed by an pushingmember (not shown). As sown in the side view, the seal 150 has alip-shaped cross section. The seal 150 having this lip-shaped crosssection contacts the dust filter 119, sealing the space defined by thedust filter 119, holder 145, optical LPF 118 and seal 150. Further,cushion members 156 are provided on the holder 145 at three points. Theysupport the dust filter 119 when an external force is exerted on theseal 150. The seal 150 contacts the dust filter 119, at its track-shapedlip part. The seal 150 therefore extends along the node area ofvibration generated in the dust filter 119 and surrounding the center ofthe dust filter 119. Hence, the seal 150 less impeding the vibration ofthe dust filter 119 than otherwise. Since the corners (and lip part) ofthe seal 150 are obtuse-angled, they will be scarcely deformed when theseal 150 receives an external force. This is why the corners of the seal150 are not arced as in the configuration of FIG. 2B.

FIG. 12 shows another modification of the vibrator 170. This modifiedvibrator 170 has a dust filter 119 is formed by cutting a circular platealong two parallel lines, forming two parallel sides. That is, themodified vibrator 170 uses a dust filter 119 that has two sidessymmetric with respect to the symmetry axis extending in theY-direction. In this case, actuate piezoelectric elements 120 a and 120b are arranged not on the straight sides, but on the curved partsdefining a circle. Since the dust filter 119 is so shaped, thepiezoelectric elements 120 a and 120 b are arranged, efficientlyproviding a smaller vibrator 170. Note that the long side and shot sideshown in FIG. 12 are the long and short sides of a virtual rectangle 175which has the same area as the dust filter 119, two opposite sides ofwhich extend along the opposite two sides of the dust filter 119,respectively. The seal 150, which is a supporting member, has arectangular cross section and made of soft material such as foamedrubber or felt. Therefore, the seal 150 attenuates the vibration only alittle as in the other embodiments. This configuration is identical tothat of FIG. 11 in any other respects, and will not be described indetail.

FIGS. 13A and 13B shows a dust-screening mechanism has a disc-shapeddust filter 119 of the conventional type and a structure for supportingand pushing a vibrator 170, the structure according to the presentembodiment. FIGS. 13A and 13B show a supporting/pushing structure thatcorresponds to the structure of FIGS. 2A and 2B, designed to support andpush a rectangular dust filter 119. Therefore, only the features thatdistinguish this embodiment from that of FIGS. 2A and 2B will bedescribed.

Three pushing mechanisms are arranged along the outer circumferentialedge of the dust filter 119 and spaced equidistantly. The dust filter119 is positioned in the X-direction and Y-direction by threepositioning members 154 arranged on, respectively, those parts of thethree pushing members 151, which are bent in the Z-direction. Thepositioning members 154 are made of vibration attenuating material, suchas rubber or resin. Each cushion member 156 is spaced from thepiezoelectric element 120 by distance AZ, in alignment with the cushionmember 153 that is provided between the pushing member 151 and the dustfilter 119. When an external force is exerted on the dust filter 119,the cushion member 156 holds the ring-shaped piezoelectric element 120arranged together with the dust filter 119, whereby the vibrator 170 issupported. The seal 150 made of rubber or soft resin is composed of aring-shaped main body 150 b and a cone-shaped lip part 150 a. The lippart 150 a extends outwards from the outer circumferential edge of themain body 150 b. The inner circumferential edge of the main body 150 bis held, pressed on the outer circumference of a ring-shaped projection145 a that is located at the rim of the opening 146 of the holder 145.In this configuration, the nodes of vibration of the dust filter 119(which are on concentric circles) exist in a focusing-beam passing area149, and control the dust filter control circuit 121, causing the sameto vibrate the vibrator in a plurality of vibrational modes of differentresonance frequencies. Since the position where the lip part 150 acontacts the dust filter 119 changes with respect to the vibrationnodes, and cannot support the dust filter 119 at all points close to thevibration nodes. Nonetheless, the loss of vibrational energy can bereduced to minimum, because the pushing force is 2 N or less as shown inFIG. 10. The cushion members 156 provided in the holder 145 are locatednear the nodes of various vibrational modes, and the vibrationalamplitude of the outer circumferential part of the dust filter 119 issmall. This decreases the loss of vibrational energy, though thepiezoelectric element 120 is mounted on the cushion members 156.

A method of removing dust will be explained in detail, with reference toFIG. 14. FIG. 14 shows a cross section identical to that shown in FIG.4B. Assume that the piezoelectric elements 120 a and 120 b are polarizedin the direction of arrow 176 as shown in FIG. 14. If a voltage of aspecific frequency is applied to the piezoelectric elements 120 a and120 b at a certain time to, the vibrator 170 will be deformed asindicated by solid lines. At the mass point Y existing at given positiony in the surface of the vibrator 170, the vibration z in the Z-directionis expressed by Equation 2, as follows:

z=A·sin(Y)·cos(ωt)  (2)

where ω is the angular velocity of vibration, A is the amplitude ofvibration in the Z-direction, and Y=2 πy/λ (λ: wavelength of bendingvibration).

The Equation 2 represents the standing-wave vibration shown in FIG. 4A.Thus, if y=s·λ/2 (here, is an integer), then Y=sπ, and sin(Y)=0. Hence,a node 177, at which the amplitude of vibration in the Z-direction iszero irrespective of time, exists for every π/2. This is standing-wavevibration. The state indicated by broken lines in FIG. 14 takes place ift=kπ/ω (k is odd), where the vibration assumes a phase opposite to thephase at time t₀.

Vibration z(Y₁) at point Y₁ on the dust filter 119 is located at anantinode 178 of standing wave, bending vibration. Hence, the vibrationin the Z-direction has amplitude A, as expressed in Equation 3, asfollows:

z(Y ₁)=A·cos(ωt)  (3)

If Equation 3 is differentiated with time, the vibration speed Vz(Y₁) atpoint Y₁ is expressed by Equation 4, below, because ω=2πf, where f isthe frequency of vibration:

$\begin{matrix}{{{Vz}( Y_{1} )} = {\frac{( {z( Y_{1} )} )}{t} = {{- 2}\pi \; {f \cdot A \cdot {\sin ( {\omega \; t} )}}}}} & (4)\end{matrix}$

If Equation 4 is differentiated with time, vibration acceleration αz(Y₁)is expressed by Equation 5, as follows:

$\begin{matrix}{{\alpha \; {z( Y_{1} )}} = {\frac{( {{Vz}( Y_{1} )} }{t} = {{- 4}\pi^{2}{f^{2} \cdot A \cdot {\cos ( {\omega \; t} )}}}}} & (5)\end{matrix}$

Therefore, the dust 179 adhering at point Y₁ receives the accelerationof Equation 5. The inertial force Fk the dust 179 receives at this timeis given by Equation 6, as follows:

Fk=αz(Y ₁)·M=−4π² f ² ·A·cos(ωt)·M  (6)

where M is the mass of the dust 179.

As can be seen from Equation 6, the inertial force Fk increases asfrequency f is raised, in proportion to the square of f. However, theinertial force cannot be increased if amplitude A is small, no matterhow much frequency f is raised. Generally, kinetic energy of vibrationcan be produced, but in a limited value, if the piezoelectric elements120 a and 120 b that produce the kinetic energy have the same size.Therefore, if the frequency is raise in the same vibrational mode,vibrational amplitude A will change in inverse proportion to the squareof frequency f. Even if the resonance frequency is raised to achieve ahigher-order resonance mode, the vibrational frequency will fall, notincreasing the vibration speed or the vibration acceleration. Rather, ifthe frequency is raised, ideal resonance will hardly be accomplished,and the loss of vibrational energy will increase, inevitably decreasingthe vibration acceleration. That is, the mode cannot attain largeamplitude if the vibration is produced in a resonance mode that useshigh frequency only. The dust removal efficiency will be much impaired.

Although the dust filter 119 is rectangular, the peak ridges 174 ofvibrational amplitude form closed loops around the optical axis in thevibrational mode of the embodiment, which is shown in FIG. 4A. In thevibrational mode of the embodiment, which is shown in FIG. 7, the peakridges 174 of vibrational amplitude form curves surrounding the midpointof each side. The wave reflected from the side extending in theX-direction and the wave reflected from the side extending in theY-direction are efficiently synthesized, forming a standing wave. Themethod of supporting the dust filter 119 in this vibrational mode isidentical to the method explained with reference to FIG. 4A. FIG. 7shows a seal contact area 180 and support areas 181. In the seal contactarea 180, the seal 150 contacts the dust filter 119. In the supportareas 181, the cushion members 156 support the dust filter 119 when anexternal force acts on the dust filter 119. The seal contact area 180and the support areas 181 are located near vibration nodes area 173 andare small areas in which the vibrational amplitude is small. Hence, theyscarcely impede the vibration generated in the dust filter 119.

The shape and size of the dust filter 119 greatly contribute toefficient generation of this synthesized standing wave. As seen fromFIG. 8, it is better to set the aspect ratio (short side/long side,i.e., ratio of the length of the short sides to that of the long sidesof the dust filter 119) to a value smaller than 1, than to 1 (to makethe dust filter 119 square). If the aspect ratio is smaller than 1, thespeed of vibration at the center of the dust filter 119, in theZ-direction will be higher (the vibration speed ratio is 0.7 or more),no matter how the piezoelectric elements 120 a and 120 b are arranged.In FIG. 8, the ratio (V/V_(max)) of the vibration speed V to the maximumvibration speed V_(max) possible in this region is plotted on theordinate. The maximum aspect ratio (i.e., short side/long side) is, ofcourse, 1. At the aspect ratio of 0.9 or less, the vibration speedabruptly decreases. Therefore, the dust filter 119 preferably has anaspect ratio (short side/long side) of 0.9 to 1, but less than 1. Thetwo dots in FIG. 8, which pertain to the case where the 120 a and 120 bare arranged parallel to the short sides of the dust filter 119,indicate vibration speed ratios, which are smaller than the vibrationspeed ratios attainable if the piezoelectric elements 120 a and 120 bare arranged parallel to the long sides of the dust filter 119. It istherefore advisable to arrange the piezoelectric elements 120 a and 120b at the long sides of the dust filter 119, not at the short sidesthereof. If the elements 120 a and 120 b are so arranged, the vibrationspeed ratio will increase to achieve a high dust removal ability. Themaximum vibration speed ratio is attained in FIG. 8 in the case wherethe vibrational mode is that of FIG. 4A and γ=+π/4 in the equation (1).

In vibration wherein the peak ridges 174 of vibrational amplitude formclosed loops around the optical axis or the peak ridges 174 form curvessurrounding the midpoint of each side, the dust filter 119 can undergovibration of amplitude a similar to that of concentric vibration thatmay occur if the dust filter 119 has a disc shape. In any vibrationalmode in which the amplitude is simply parallel to the side, thevibration acceleration is only 10% or more of the acceleration achievedin this embodiment.

In the vibration wherein the peak ridges 174 of vibrational amplitudeform closed loops or curves surrounding the midpoint of each side, thevibrational amplitude is the largest at the center of the vibrator 170and small at the closed loop or the curve at circumferential edges.Thus, the dust removal capability is maximal at the center of the image.If the center of the vibrator 170 is aligned with the optical axis, theshadow of dust 179 will not appear in the center part of the image,which has high image quality. This is an advantage.

In the vibration node areas 173, which exist in the focusing-beampassing area, the nodes 177 may be changed in position by changing thedrive frequencies of the piezoelectric elements 120 a and 120 b. Then,the elements 120 a and 120 b resonate in a different vibrational mode,whereby the dust can be removed, of course.

A vibration state that is attained if the piezoelectric elements 120 aand 120 b are driven at a frequency near the resonance frequency will bedescribed with reference to FIGS. 15A and 15B. FIG. 15A shows anequivalent circuit that drives the piezoelectric elements 120 a and 120b at a frequency near the resonance frequency. In FIG. 15A, C₀ is theelectrostatic capacitance attained as long as the piezoelectric elements120 a and 120 b remain connected in parallel, and L, C and R are thevalues of a coil, capacitor and resistor that constitute an electriccircuit equivalent to the mechanical vibration of the vibrator 170.Naturally, these values change with the frequency.

When the frequency changes to resonance frequency f₀, L and C achieveresonance as is illustrated in FIG. 15B. As the frequency is graduallyraised toward the resonance frequency from the value at which noresonance takes place, the vibration phase of the vibrator 170 changeswith respect to the phase of vibration of the piezoelectric elements 120a and 120 b. When the resonance starts, the phase reaches π/2. As thefrequency is further raised, the phase reaches π. If the frequency israised even further, the phase starts decreasing. When the frequencycomes out of the resonance region, the phase becomes equal to the phasewhere no resonance undergoes at low frequencies. In the actualsituation, however, the vibration state does not become ideal. The phasedoes not change to π in some cases. Nonetheless, the drive frequency canbe set to the resonance frequency.

Support areas 181 existing at the four corners, which are shown in FIG.4A, FIG. 6B and FIG. 7, are areas in which virtually no vibration takesplace. Therefore, when pushed in Z direction with an external force,these parts hold the dust filter 119 through the cushion members 156that are made of vibration-attenuating material such as rubber. So held,the dust filter 119 can be reliably supported without attenuating thevibration, because the lip part 150 a of the seal 150 displaces only alittle and the pushing force of the seal 150 does not increase.Moreover, the lip part 150 a reliably restores its initial shape when itis released from the external force. Made of rubber or the like, thecushion members 153 can allow the dust filter 119 to vibrate in planeand never attenuate the in-plane vibration of the dust filer. The usermay remove the exchange lens and may then remove fine dust particlesfrom the surface of the dust filter 119, using a cleaning device. Whilebeing so cleaned, the dust filter 119 may receive an external force. Inthis case, the external force would act directly on the seal 150,twisting the seal 150, if the supporting/pushing structure had not theconfiguration according to this embodiment. Even after released from theexternal force, the lip part 150 a of the seal 150 should remaindeformed, not restoring its initial shape. The dust filter 119 must becleaned for the following reason. That is, fine dust particles and fineliquid particles cannot be removed by vibrating the dust filter 119, aswill be explained later. Many fine dust particles remaining on the dustfilter 119 lower the transmittance the dust filter 119 has with respectto a focusing-beam, as will be explained later. Hence, the surface ofthe dust filter 119 must be cleaned if it is excessively unclean withfine dust particles or fine liquid particles.

On the other hand, the seal 150 must be provided in the area havingvibrational amplitude, too. In the vibrational mode of the presentinvention, the peripheral vibrational amplitude is small. In view ofthis, the lip part 150 a of the seal 150 holds the circumferential partof the dust filter 119 and receives a small pressing force. As a result,the force does not greatly act in the amplitude direction of bendingvibration. Therefore, the seal 156 attenuates, but very little, thevibration whose amplitude is inherently small. As shown in FIG. 4A, FIG.6 and FIG. 9, as many seal-contact parts 180 as possible contact thenode areas 173 in which the vibrational amplitude is small. This furtherreduces the attenuation of vibration.

The prescribed frequency at which to vibrate the piezoelectric elements120 a and 120 b is determined by the shape, dimensions, material andsupported state of the dust filter 119, which is one component of thevibrator 170. In most cases, the temperature influences the elasticitycoefficient of the vibrator 170 and is one of the factors that changethe natural frequency of the vibrator 170. Therefore, it is desirable tomeasure the temperature of the vibrator 170 and to consider the changein the natural frequency of the vibrator 170, before the vibrator 170 isused. A temperature sensor (not shown) is therefore connected to atemperature measuring circuit (not shown), in the digital camera 10. Thevalue by which to correct the vibrational frequency of the vibrator 170in accordance with the temperature detected by the temperature sensor isstored in the nonvolatile memory 128. Then, the measured temperature andthe correction value are read into the Bucom 101. The Bucom 101calculates a drive frequency, which is used as drive frequency of thedust filter control circuit 121. Thus, vibration can be produced, whichis efficient with respect to temperature changes, as well.

The dust filter control circuit 121 of the digital camera 10 accordingto this invention will be described below, with reference to FIGS. 16and 17. The dust filter control circuit 121 has such a configuration asshown in FIG. 16. The components of the dust filter control circuit 121produce signals (Sig1 to Sig4) of such waveforms as shown in the timingchart of FIG. 17. These signals will control the dust filter 119, aswill be described below.

More specifically, as shown in FIG. 16, the dust filter control circuit121 comprises a N-scale counter 182, a half-frequency dividing circuit183, an inverter 184, a plurality of MOS transistors Q₀₀, Q₀₁ and Q₀₂, atransformer 185, and a resistor R₀₀.

The dust filter control circuit 121 is so configured that a signal(Sig4) of the prescribed frequency is produced at the secondary windingof the transformer 185 when MOS transistors Q₀₁ and Q₀₂ connected to theprimary winding of the transformer 185 are turned on and off. The signalof the prescribed frequency drives the piezoelectric elements 120 a and120 b, thereby causing the vibrator 170, to which the dust filter 119 issecured, to produce a resonance standing wave.

The Bucom 101 has two output ports P_PwCont and D_NCnt provided ascontrol ports, and a clock generator 186. The output ports P_PwCont andD_NCnt and the clock generator 186 cooperate to control the dust filtercontrol circuit 121 as follows. The clock generator 186 outputs a pulsesignal (basic clock signal) having a frequency much higher than thefrequency of the signal that will be supplied to the piezoelectricelements 120 a and 120 b. This output signal is signal Sig1 that has thewaveform shown in the timing chart of FIG. 17. The basic clock signal isinput to the N-scale counter 182.

The N-scale counter 182 counts the pulses of the pulse signal. Everytime the count reaches a prescribed value “N,” the N-scale counter 182produces a count-end pulse signal. Thus, the basic clock signal isfrequency-divided by N. The signal the N-scale counter 182 outputs issignal Sig2 that has the waveform shown in the timing chart of FIG. 17.

The pulse signal produced by means of frequency division does not have aduty ratio of 1:1. The pulse signal is supplied to the half-frequencydividing circuit 183. The half-frequency dividing circuit 183 changesthe duty ratio of the pulse signal to 1:1. The pulse signal, thuschanged in terms of duty ratio, corresponds to signal Sig3 that has thewaveform shown in the timing chart of FIG. 17.

While the pulse signal, thus changed in duty ratio, is high, MOStransistor Q₀₁ to which this signal has been input is turned on. In themeantime, the pulse signal is supplied via the inverter 184 to MOStransistor Q₀₂. Therefore, while the pulse signal (signal Sig3) is lowstate, MOS transistor Q₀₂ to which this signal has been input is turnedon. Thus, the transistors Q₀₁ and Q₀₂, both connected to the primarywinding of the transformer 185, are alternately turned on. As a result,a signal Sig4 of such frequency as shown in FIG. 17 is produced in thesecondary winding of the transformer 185.

The winding ratio of the transformer 185 is determined by the outputvoltage of the power-supply circuit 135 and the voltage needed to drivethe piezoelectric elements 120 a and 120 b. Note that the resistor R₀₀is provided to prevent an excessive current from flowing in thetransformer 185.

In order to drive the piezoelectric elements 120 a and 120 b, MOStransistor Q₀₀ must be on, and a voltage must be applied from thepower-supply circuit 135 to the center tap of the transformer 185. Inthis case, MOS transistor Q₀₀ is turned on or off via the output portP_PwCont of the Bucom 101. Value “N” can be set to the N-scale counter182 from the output port D_NCnt of the Bucom 101. Thus, the Bucom 101can change the drive frequency for the piezoelectric elements 120 a and120 b, by appropriately controlling value “N.”

The frequency can be calculated by using Equation 7, as follows:

$\begin{matrix}{{fdrv} = \frac{fpls}{2N}} & (7)\end{matrix}$

where N is the value set to the N-scale counter 182, fpls is thefrequency of the pulse output from the clock generator 186, and fdrv isthe frequency of the signal supplied to the piezoelectric elements 120 aand 120 b.

The calculation based on Equation 7 is performed by the CPU (controlunit) of the Bucom 101.

If the dust filter 119 is vibrated at a frequency in the ultrasonicregion (i.e., 20 kHz or more), the operating state of the dust filter119 cannot be aurally discriminated, because most people cannot hearsound falling outside the range of about 20 to 20,000 Hz. This is whythe operation display LCD 129 or the operation display LED 130 has adisplay unit for showing how the dust filter 119 is operating, to theoperator of the digital camera 10. More precisely, in the digital camera10, the vibrating members (piezoelectric elements 120 a and 120 b)imparts vibration to the dust-screening member (dust filter 119) that isarranged in front of the CCD 117, can be vibrated and can transmitlight. In the digital camera 10, the display unit is operated ininterlock with the vibrating member drive circuit (i.e., dust filtercontrol circuit 121), thus informing how the dust filter 119 isoperating (later described in detail).

To explain the above-described characteristics in detail, the controlthe Bucom 101 performs will be described with reference to FIGS. 18A to22. FIGS. 18A and 18B show the flowchart that relates to the controlprogram, which the Bucom 101 starts executing when the power switch (notshown) provided on the body unit 100 of the camera 10 is turned on.

First, a process is performed to activate the digital camera 10 (StepS101). That is, the Bucom 101 control the power-supply circuit 135. Socontrolled, the power-supply circuit 135 supplies power to the othercircuit units of the digital camera 10. Further, the Bucom 101initializes the circuit components.

Next, the Bucom 101 calls a sub-routine “silent vibration,” vibratingthe dust filter 119, making no sound (that is, at a frequency fallingoutside the audible range) (Step S102). The “audible range” ranges fromabout 200 to 20,000 Hz, because most people can hear sound fallingwithin this range.

Steps S103 to S124, which follow, make a group of steps that iscyclically repeated. That is, the Bucom 101 first detects whether anaccessory has been attached to, or detached from, the digital camera 10(Step S103). Whether the lens unit 200 (i.e., one of accessories), forexample, has been attached to the body unit 100 is detected. Thisdetection, e.g., attaching or detaching of the lens unit 200, isperformed as the Bucom 101 communicates with the Lucom 201.

If a specific accessory is detected to have been attached to the bodyunit 100 (YES in Step S104), the Bucom 101 calls a subroutine “silentvibration” and causes the dust filter 119 to vibrate silently (StepS105).

While an accessory, particularly the lens unit 200, remains not attachedto the body unit 100 that is the camera body, dust is likely to adhereto each lens, the dust filter 119, and the like. It is thereforedesirable to perform an operation of removing dust at the time when itis detected that the lens unit 200 is attached to the body unit 100. Itis highly possible that dust adheres as the outer air circulates in thebody unit 100 at the time a lens is exchanged with another. It istherefore advisable to remove dust when a lens is exchange with another.Then, it is determined that photography will be immediately performed,and the operation goes to Step S106.

If a specific accessory is not detected to have been attached to thebody unit 100 (NO in Step S104), the Bucom 101 goes to the next step,i.e., Step S106.

In Step S106, the Bucom 101 detects the state of a specific operationswitch that the digital camera 10 has.

That is, the Bucom 101 determines whether the first release switch (notshown), which is a release switch, has been operated from the on/offstate of the switch (Step S107). The Bucom 101 reads the state. If thefirst release switch has not been turned on for a predetermined time,the Bucom 101 discriminates the state of the power switch (Step S108).If the power switch is on, the Bucom 101 returns to Step S103. If thepower switch is off, the Bucom 101 performs an end-operation (e.g.,sleep).

On the other hand, the first release switch may be found to have beenturned on in Step S107. In this case, the Bucom 101 acquires theluminance data about the object, from the photometry circuit 115, andcalculates from this data an exposure time (Tv value) and a diaphragmvalue (Av value) that are optimal for the image acquisition unit 116 andlens unit 200, respectively (Step S109).

Thereafter, the Bucom 101 acquires the detection data from the AF sensorunit 109 through the AF sensor drive circuit 110, and calculates adefocus value from the detection data (Step S110). The Bucom 101 thendetermines whether the defocus value, thus calculated, falls within apreset tolerance range (Step S111). If the defocus value does not fallwithin the tolerance range, the Bucom 101 drives the photographic lens202 (Step S112) and returns to Step S103.

On the other hand, the defocus value may falls within the tolerancerange. In this case, the Bucom 101 calls the subroutine “silentvibration” and causes the dust filter 119 to vibrate silently (StepS113).

Further, the Bucom 101 determines whether the second release switch (notshown), which is another release switch, has been operated (Step S114).If the second release switch is on, the Bucom 101 goes to Step S115 andstarts the prescribed photographic operation (later described indetail). If the second release switch is off, the Bucom 101 returns toStep S108.

During the image acquisition operation, the electronic image acquisitionis controlled for a time that corresponds to the preset time forexposure (i.e., exposure time), as in ordinary photography.

As the above-mentioned photographic operation, Steps S115 to S121 areperformed in a prescribed order to photograph an object. First, theBucom 101 transmits the Av value to the Lucom 201, instructing the Lucom201 to drive the diaphragm 203 (Step S115). Thereafter, the Bucom 101moves the quick return mirror 105 to the up position (Step S116). Then,the Bucom 101 causes the front curtain of the shutter 108 to startrunning, performing open control (Step S117). Further, the Bucom 101makes the image process controller 126 perform “image acquisitionoperation” (Step S118). When the exposure to the CCD 117 (i.e.,photography) for the time corresponding to the Tv value ends, the Bucom101 causes the rear curtain of the shutter 108 to start running,achieving CLOSE control (Step S119). Then, the Bucom 101 drives thequick return mirror 105 to the down position and cocks the shutter 108(Step S120).

Then, the Bucom 101 instructs the Lucom 210 to move the diaphragm 203back to the open position (Step S121). Thus, a sequence of imageacquisition steps is terminated.

Next, the Bucom 101 determines whether the recording medium 127 isattached to the body unit 100 (Step S122). If the recording medium 127is not attached, the Bucom 101 displays an alarm (Step S123). The Bucom101 then returns to Step S103 and repeats a similar sequence of steps.

If the recording medium 127 is attached, the Bucom 101 instructs theimage process controller 126 to record the image data acquired byphotography, in the recording medium 127 (Step S124). When the imagedata is completely recorded, the Bucom 101 returns to Step S103 againand repeats a similar sequence of steps.

In regard to the detailed relation between the vibration state and thedisplaying state will be explained in detail, the sequence ofcontrolling the “silent vibration” subroutine will be explained withreference to FIGS. 19 to 22. The term “vibration state” means the stateof the vibration induced by the piezoelectric elements 120 a and 120 b,i.e., vibrating members. FIG. 23 shows the form of a resonance-frequencywave that is continuously supplied to the vibrating members duringsilent vibration. The subroutine of FIG. 19, i.e., “silent vibration,”and the subroutine of FIGS. 20 to 22, i.e., “display process” areroutines for accomplishing vibration exclusively for removing dust fromthe dust filter 119. Vibrational frequency f₀ is set to a value close tothe resonance frequency of the dust filter 119. In the vibrational modeof FIG. 4A, for example, the vibrational frequency is 91 kHz, higherthan at least 20 kHz, and produces sound not audible to the user.

As shown in FIG. 19, when the “silent vibration” is called, the Bucom101 first reads the data representing the drive time (Toscf0) and drivefrequency (resonance frequency: Noscf0) from the data stored in aspecific area of the nonvolatile memory 128 (Step S201). At this timing,the Bucom 101 causes the display unit provided in the operation displayLCD 129 or operation display LED 130 to turn on the vibrational modedisplay, as shown in FIG. 20 (Step S301). The Bucom 101 then determineswhether a predetermined time has passed (Step S302). If thepredetermined time has not passed, the Bucom 101 makes the display unitkeep turning on the vibrational mode display. Upon lapse of thepredetermined time, the Bucom 101 turns off the displaying of thevibrational mode display (Step S303).

Next, the Bucom 101 outputs the drive frequency Noscf0 from the outputport D_NCnt to the N-scale counter 182 of the dust filter controlcircuit 121 (Step S202).

In the following steps S203 to S205, the dust is removed as will bedescribed below. First, the Bucom 101 sets the output port P_PwCont toHigh, thereby starting the dust removal (Step S203). At this timing, theBucom 101 starts displaying the vibrating operation as shown in FIG. 21(Step S311). The Bucom 101 then determines whether or not thepredetermined time has passed (Step S312). If the predetermined time hasnot passed, the Bucom 101 keeps displaying the vibrating operation. Uponlapse of the predetermined time, the Bucom 101 stops displaying of thevibrating operation (Step S313). The display of the vibrating operation,at this time, changes as the time passes or as the dust is removed (howit changes is not shown, though). The predetermined time is almost equalto Toscf0, i.e., the time for which the vibration (later described)continues.

If the output port P_PwCont is set to High in Step S203, thepiezoelectric elements 120 a and 120 b vibrate the dust filter 119 atthe prescribed vibrational frequency (Noscf0), removing the dust 179from the surface of the dust filter 119. At the same time the dust isremoved from the surface of the dust filter 119, air is vibrated,producing an ultrasonic wave. The vibration at the drive frequencyNoscf0, however, does not make sound audible to most people. Hence, theuser hears nothing. The Bucom 101 waits for the predetermined timeToscf0, while the dust filter 119 remains vibrated (Step S204). Uponlapse of the predetermined time Toscf0, the Bucom 101 sets the outputport P_PwCont to Low, stopping the dust removal operation (Step S205).At this timing, the Bucom 101 turns on the display unit, whereby thedisplaying of the vibration-end display is turned on (Step S321). Whenthe Bucom 101 determines (in Step S322) that the predetermined time haspassed, the displaying of the vibration-end display is turned off (StepS323). The Bucom 101 then returns to the step next to the step in whichthe “silent vibration” is called.

The vibrational frequency f₀ (i.e., resonance frequency Noscf0) and thedrive time (Toscf0) used in this subroutine define such a waveform asshown in the graph of FIG. 23. As can be seen from this waveform,constant vibration (f₀=91 kHz) continues for a time (i.e., Toscf0) thatis long enough to accomplish the dust removal.

That is, the vibrational mode adjusts the resonance frequency applied tothe vibrating member, controlling the dust removal.

Second Embodiment

The subroutine “silent vibration” called in the camera sequence (mainroutine) that the Bucom performs in a digital camera that is a secondembodiment of the image equipment according to this invention will bedescribed with reference to FIG. 24. FIG. 24 illustrates a modificationof the subroutine “silent vibration” shown in FIG. 17. The secondembodiment differs from the first embodiment in the operating mode ofthe dust filter 119. In the first embodiment, the dust filter 119 isdriven at a fixed frequency, i.e., frequency f₀, producing a standingwave. By contrast, in the second embodiment, the drive frequency isgradually changed, thereby achieving large-amplitude vibration atvarious frequencies including the resonance frequency, without strictlycontrolling the drive frequency.

If the aspect ratio shown in FIG. 8 has changed from the design value of0.9, during the manufacture, the vibrational mode will greatly change(that is, the vibration speed ratio will abruptly change). Therefore, aprecise resonance frequency must be set in each product and thepiezoelectric elements 120 a and 120 b must be driven at the frequencyso set. This is because the vibration speed will further decrease if thepiezoelectric elements are driven at any frequency other than theresonance frequency. An extremely simple circuit configuration can,nonetheless, drive the piezoelectric elements precisely at the resonancefrequency if the frequency is controlled as in the second embodiment. Amethod of control can therefore be achieved to eliminate any differencein resonance frequency between the products.

In the subroutine “silent vibration” of FIG. 24, the vibrationalfrequency f₀ is set to a value close to the resonance frequency of thedust filter 119. The vibrational frequency f₀ is 91 kHz in, for example,the vibrational mode of FIG. 4A. That is, the vibrational frequencyexceeds at least 20 kHz, and makes sound not audible to the user.

First, the Bucom 101 reads the data representing the drive time(Toscf0), drive-start frequency (Noscfs), frequency change value (Δf)and drive-end frequency (Noscft), from the data stored in a specificarea of the nonvolatile memory 128 (Step S211). At this timing, theBucom 101 causes the display unit to display the vibrational mode asshown in FIG. 20, in the same way as in the first embodiment.

Next, the Bucom 101 sets the drive-start frequency (Noscfs) as drivefrequency (Noscf) (Step S212). The Bucom 101 then outputs the drivefrequency (Noscf) from the output port D_NCnt to the N-scale counter 182of the dust filter control circuit 121 (Step S213).

In the following steps S203 et seq., the dust is removed as will bedescribed below. First, the dust removal is started. At this time, thedisplay of the vibrating operation is performed as shown in FIG. 21, asin the first embodiment.

First, the Bucom 101 sets the output port P_PwCont to High, to achievedust removal (Step S214). The piezoelectric elements 120 a and 120 bvibrate the dust filter 119 at the prescribed vibrational frequency(Noscf), producing a standing wave of a small amplitude at the dustfilter 119. The dust cannot be removed from the surface of the dustfilter 119, because the vibrational amplitude is small. This vibrationcontinues for the drive time (Toscf0) (Step S215). Upon lapse of thisdrive time (Toscf0), the Bucom 101 determines whether the drivefrequency (Noscf) is equal to the drive-end frequency (Noscft) (StepS216). If the drive frequency is not equal to the drive-end frequency(NO in Step S216), the Bucom 101 adds the frequency change value (Δf) tothe drive frequency (Noscf), and sets the sum to the drive frequency(Noscf) (Step S217). Then, the Bucom 101 repeats the sequence of StepsS212 to S216.

If the drive frequency (Noscf) is equal to the drive-end frequency(Noscft) (YES in Step S216), the Bucom 101 sets the output port P_PwContto Low, stopping the vibration of the piezoelectric elements 120 a and120 b (Step S218), thereby terminating the “silent vibration.” At thispoint, the display of vibration-end is performed as shown in FIG. 22, asin the first embodiment.

As the frequency is gradually changed as described above, the amplitudeof the standing wave increases. In view of this, the drive-startfrequency (Ncoscfs), the frequency change value (Δf) and the drive-endfrequency (Noscft) are set so that the resonance frequency of thestanding wave may be surpassed. As a result, a standing wave of smallvibrational amplitude is produced at the dust filter 119. The standingwave can thereby controlled, such that its vibrational amplitudegradually increases until it becomes resonance vibration, and thendecreases thereafter. If the vibrational amplitude (corresponding tovibration speed) is larger than a prescribed value, the dust 179 can beremoved. In other words, the dust 179 can be removed while thevibrational frequency remains in a prescribed range. This range is broadin the present embodiment, because the vibrational amplitude is largeduring the resonance.

If the difference between the drive-start frequency (Noscfs) and thedrive-end frequency (Noscft) is large, the fluctuation of the resonancefrequency, due to the temperature of the vibrator 170 or to thedeviation in characteristic change of the vibrator 170, during themanufacture, can be absorbed. Hence, the dust 179 can be reliablyremoved from the dust filter 119, by using an extremely simple circuitconfiguration.

The present invention has been explained, describing some embodiments.Nonetheless, this invention is not limited to the embodiments describedabove. Various changes and modifications can, of course, be made withinthe scope and spirit of the invention.

For example, a mechanism that applies an air flow or a mechanism thathas a wipe may be used in combination with the dust removal mechanismhaving the vibrating member, in order to remove the dust 179 from thedust filter 119.

In the embodiments described above, the vibrating members arepiezoelectric elements. The piezoelectric elements may be replaced byelectrostrictive members or super nagnetostrictive elements. In theembodiments, two piezoelectric elements 120 a and 120 b are secured tothe dust filter 119 that is dust-screening member. Instead, only onepiezoelectric element may be secured to the dust filter 119. In thiscase, that side of the dust filter 119, to which the piezoelectricelement is secured, differs in rigidity from the other side of the dustfilter 119. Consequently, the node areas 173 where vibrational amplitudeis small will form a pattern similar to that of FIG. 4A, FIG. 6B or FIG.7, but will be dislocated. Thus, it is desirable to arrange twopiezoelectric elements symmetrical to each other, because the vibrationcan be produced more efficiently and the dust filter 119 can be moreeasily held at four corners.

In order to remove dust more efficiently from the member vibrated, themember may be coated with an indium-tin oxide (ITO) film, which is atransparent conductive film, indium-zinc film, poly 3,4-ethylenedioxythiophene film, surfactant agent film that is a hygroscopicanti-electrostatic film, siloxane-based film, or the like. In this case,the frequency, the drive time, etc., all related to the vibration, areset to values that accord with the material of the film.

Moreover, the optical LPF 118, described as one embodiment of theinvention, may be replaced by a plurality of optical LPFs that exhibitbirefringence. Of these optical LPFs, the optical LPF located closest tothe object of photography may be used as a dust-screening member (i.e.,a subject to be vibrated), in place of the dust filter 119 shown in FIG.2A.

Further, a camera may does not have the optical LPF 118 of FIG. 2Adescribed as one embodiment of the invention, and the dust filter 119may be used as an optical element such as an optical LPF, aninfrared-beam filter, a deflection filter, or a half mirror.

Furthermore, the camera may not have the optical LPF 118, and the dustfilter 119 may be replaced by the protection glass plate 142 shown inFIG. 2A. In this case, the protection glass plate 142 and the CCD chip136 remain free of dust and moisture, and the structure of FIG. 2A thatsupports and yet vibrates the dust filter 119 may be used to support andvibrate the protection glass plate 142. Needless to say, the protectionglass plate 142 may be used as an optical element such as an opticalLPF, an infrared-beam filter, a deflection filter, or a half mirror.

The image equipment according to this invention is not limited to theimage acquisition apparatus (digital camera) exemplified above. Thisinvention can be applied to any other apparatus that needs a dustremoval function. The invention can be practiced in the form of variousmodifications, if necessary. More specifically, a dust moving mechanismaccording to this invention may be arranged between the display elementand the light source or image projecting lens in an image projector.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A vibrating device comprising: a dust-screening member shaped like aplate as a whole; a vibrating member arranged outside the dust-screeningmember and configured to produce, at the dust-screening member,vibration having a vibrational amplitude perpendicular to a surface ofthe dust-screening member; a counter member spaced apart from thatsurface of the dust-screening member, on which the vibrating member isarranged; a pushing member configured to push the dust-screening memberonto the counter member; and a first support member arranged between thecounter member and the dust-screening member, surrounding a center ofthe dust-screening member, and configured to support the dust-screeningmember when pushed by the pushing member, wherein the first supportmember is pushed with a pressure of 2 N or less when the pushing memberpushes the first support member.
 2. The device according to claim 1,further comprising: a second support member configured to support one ofthe dust-screening member and the vibrating member in a node areawherein vibration scarcely has amplitudes perpendicular to the surfaceof the dust-screening member, when an external force is applied,exerting a pressure on the dust-screening member and deforming the firstsupport member to a prescribed extent.
 3. The device according to claim2, wherein the rigidity that the second support member has in thepushing direction is higher than the rigidity that the first supportmember has in the pushing direction.
 4. The device according to claim 2,wherein the position where the first support member supports thedust-screening member is closer to the center of the dust-screeningmember than the position where the second support member supports one ofthe dust-screening member and the vibrating member.
 5. The deviceaccording to claim 1, wherein the first support member almost seals aspace existing between the dust-screening member and the counter member.6. The device according to claim 1, wherein the dust-screening memberhas at least one side and has a shape symmetric to an axis perpendicularto the side, the device further comprises a drive unit configured todrive the vibrating member to produce vibration Z (x, y) at thedust-screening member, the vibration being expressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{mn}( {x,y} )} = {{\sin ( {{n\mspace{2mu} {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{m\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};$${{W_{n\; m}( {x,y} )} = {{\sin ( {{m\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{n\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};$and γ is +π/4 or ranges from −π/8 to −π/4, and the dust-screening memberis shaped such that the ratio of length of either short side to eitherlong side of a virtual rectangle is 0.9 or more, but less than 1, thevirtual rectangle having the same area as the dust-screening member andhaving sides including the one side which the dust-screening member has.7. The device according to claim 6, wherein the vibrating member isarranged on the dust-screening member at prescribed position near thelonger side of the virtual rectangle.
 8. The device according to claim6, wherein when γ is +π/4, vibration produced at the dust-screeningmember by the drive unit is vibration such that peak ridges of thevibration having a vibrational amplitude perpendicular to the surface ofthe dust-screening member form closed loops.
 9. The device according toclaim 6, wherein when γ ranges from −π/8 to −π/4, vibration produced atthe dust-screening member by the drive unit is vibration such that peakridges of the vibration having a vibrational amplitude perpendicular tothe surface of the dust-screening member form curves around a midpointof the side which the dust-screening member has.
 10. The deviceaccording to claim 6, wherein the vibrating member includes apiezoelectric element, and the drive unit supplies a signal to thepiezoelectric element to produce the vibration at the dust-screeningmember, the signal having a frequency that accords with a size andmaterial of the dust-screening member.
 11. The device according to claim10, wherein the drive unit supplies a signal to the piezoelectricelement at prescribed time intervals, the signal changing in frequency,from a drive-start frequency to a drive-end frequency in increments of agiven transmutation frequency, including the frequency that accords withthe with size and material of the dust-screening member.
 12. The deviceaccording to claim 6, wherein a plurality of vibrating members areprovided on the dust-screening member.
 13. An image equipmentcomprising: an image forming element having an image surface on which anoptical image is formed; a dust-screening member shaped like a plate asa whole, having a light-transmitting region at least spreading to apredetermined region, facing the image surface and spaced therefrom by apredetermined distance; a vibrating member configured to producevibration having an amplitude perpendicular to a surface of thedust-screening member, the vibrating member being provided on thedust-screening member, outside the light-transmitting region throughwhich a light beam forming an optical image on the image surface passes;a counter member spaced apart from the dust-screening member; and afirst support member arranged between the counter member and thedust-screening member, surrounding a center of the dust-screeningmember, and configured to support the dust-screening member when pushedby the dust-screening member, wherein the first support member is pushedwith a pressure of 2 N or less.
 14. The equipment according to claim 13,further comprising: a second support member configured to support one ofthe dust-screening member and the vibrating member in a node areawherein vibration scarcely has amplitudes perpendicular to the surfaceof the dust-screening member, when an external force is applied,exerting a pressure on the dust-screening member and deforming the firstsupport member to a prescribed extent.
 15. The equipment according toclaim 14, wherein the rigidity that the second support member has in thepushing direction is higher than the rigidity that the first supportmember has in the pushing direction.
 16. The equipment according toclaim 14, wherein the position where the first support member supportsthe dust-screening member is closer to the center of the dust-screeningmember than the position where the second support member supports one ofthe dust-screening member and the vibrating member.
 17. The equipmentaccording to claim 13, wherein the first support member almost seals aspace existing between the dust-screening member and the counter memberand defined by the image forming element and the dust-screening memberwhich oppose each other.
 18. The equipment according to claim 13,wherein the dust-screening member has at least one side and has a shapesymmetric to an axis perpendicular to the side, the equipment furthercomprises a drive unit configured to drive the vibrating member toproduce vibration Z (x, y) at the dust-screening member, the vibrationbeing expressed as follows:Z(x,y)=W _(mn)(x,y)·cos(γ)+W _(nm)(x,y)·sin(γ) where Z (x, y) isvibration at a given point P (x, y) on the dust-screening member; m andn are positive integers including 0, indicating the order of naturalvibration corresponding to a vibrational mode;${{W_{mn}( {x,y} )} = {{\sin ( {{n\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{m\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};$${{W_{n\; m}( {x,y} )} = {{\sin ( {{m\; {\pi \cdot x}} + \frac{\pi}{2}} )} \cdot {\sin ( {{n\; {\pi \cdot y}} + \frac{\pi}{2}} )}}};$and γ is +π/4 or ranges from −π/8 to −π/4, and the dust-screening memberis shaped such that the ratio of length of either short side to eitherlong side of a virtual rectangle is 0.9 or more, but less than 1, thevirtual rectangle having the same area as the dust-screening member andhaving sides including the one side which the dust-screening member has.19. The equipment according to claim 18, wherein the vibrating member isarranged on the dust-screening member at prescribed position near thelonger side of the virtual rectangle.
 20. The equipment according toclaim 18, wherein when γ is +π/4, the drive unit produces at thedust-screening member vibration such that peak ridges of the vibrationhaving a vibrational amplitude perpendicular to the surface of thedust-screening member form closed loops around an optical axis thatpasses the image surface of the image forming element.
 21. The equipmentaccording to claim 18, wherein when γ is −π/8 to −π/4, the drive unitproduces at the dust-screening member vibration such that peak ridges ofthe vibration having a vibrational amplitude perpendicular to thesurface of the dust-screening member form curves surrounding a midpointof the side which the dust-screening member has.
 22. The equipmentaccording to claim 18, wherein the vibrating member includes apiezoelectric element, and the drive unit supplies a signal to thepiezoelectric element to produce the vibration at the dust-screeningmember, the signal having a frequency that accords with a size andmaterial of the dust-screening member.
 23. The equipment according toclaim 22, wherein the drive unit supplies a signal to the piezoelectricelement at prescribed time intervals, the signal changing in frequency,from a drive-start frequency to a drive-end frequency in increments of agiven transmutation frequency, including the frequency that accords withthe with size and material of the dust-screening member.
 24. Theequipment according to claim 18, wherein a plurality of vibratingmembers are provided on the dust-screening member and surround the beampassing area of the dust-screening member.